This invention relates to coating compositions and in particular to corrosion resistant primer compositions.
Primer compositions containing borates as corrosion inhibitive pigments are known in the art as shown by Orth, Jr., U.S. Pat. No. 2,809,949, issued Oct. 15, 1957; Russell Jr., U.S. Pat. No. 3,287,142, issued Nov. 22, 1966; Robinson, U.S. Pat. No. 3,380,836, issued Apr. 30, 1968 and Goodell, U.S. Pat. No. 3,829,395, issued Aug. 13, 1974. Thus, the primer compositions disclosed in the aforementioned patents employ borates such as sodium borates, barium borates including barium metaborates, calcium metaborate, and zinc borate as corrosion inhibitive pigments. Moreover, U.S. Pat. No. 3,287,142 to Russell, Jr. discloses a protective coating composition containing a mixture of a metal dust such as powdered zinc or lead and barium borate as corrosion inhibiting pigments. However, none of these prior art patents disclose or suggest that blends of zinc borate and barium metaborate would be particularly efficacious as corrosion inhibiting pigments and in fact in the present state of the art, zinc borate is regarded as the best corrosion inhibitive pigment with the other borates being noted as less effective. Accordingly, it was completely surprising and unexpected in accordance with this invention to find that when blends of zinc borate and barium metaborate are employed a corrosion inhibitive pigments 1n certain resinous film forming vehicle compositions corrosion resistance was markedly and synergistically enhanced when compared to the same compositions containing zinc borate or barium metaborate alone.